I would say most of the gain I got was from fixing the burnt valve and doing a mild porting and polishing of the head. After running with the audio knock sensor for a while after doing it I pretty much figured that shaving the head caused more tuning issues than the gain it gave me. It will also take a lot of your bottom end power away and make it suck under 1500rpms if you want to keep the knock halfway under control.
With a stock computer and no knock sensor it might not be apparent but I bet the engine won't last as long with a shaved head. It would have a much higher chance of bottom end failure from the knock. I would guess 75-100k miles. My setup has a pretty good bit of information available to help tune out the knock and even with 93 octane it cant take more than 1/4 throttle under 2000rpm. That was with the timing at -10 degrees so it is mainly compression causing the knock and not spark timing. 020 might be ok to try but really with a year of messing with a shaved head I am pretty much ready to give up on it. Unless I can get a reliable water injection system working then I will want to shave a bit more off
